1. Field of the Invention
The present invention relates to photosensitive polymers and to chemically amplified resist compositions. More particularly, the present invention relates to photosensitive polymers which includes a copolymer containing adamantylalkyl vinyl ether, and to resist compositions which include the photosensitive polymer.
2. Description of the Related Art
As semiconductor devices become highly integrated, photolithography processes used in the manufacture of such devices must be capable of forming fine patterns. For example, 0.2 xcexcm or smaller sized patterns are needed for semiconductor memory devices having capacities exceeding 1 Gbit. Accordingly, conventional resist materials have limited applicability since they are utilized in conjunction with krypton flouride (KrF) excimer lasers having wavelengths (248 nm) which are too large for use in the formation of ultra-fine patterns. Thus, new resist materials have been proposed for use in conjunction with an argon flouride (ArF) excimer laser. This is because the ArF excimer laser has a wavelength (193 nm) which is smaller than that of the KrF excimer laser.
Present resist materials designed for use with ArF excimer lasers suffer several drawbacks as compared with conventional resist materials. The most common of these problems are low transmittance and poor resistance to dry etching.
Acryl- or methacryl-based polymers are generally used and known as ArF resist materials. Representative examples of such polymers include poly(methacrylate)-based polymer materials. However, such polymers exhibit, amount other potential drawbacks, a poor resistance to dry etching. The selectivity of these materials is generally too low to perform a dry etching process using a plasma gas.
Accordingly, in an effort to enhance dry etching resistance, alicyclic compounds having a strong resistance to dry etching, for example, an isobornyl, adamantyl or tricyclodecanyl group, may be introduced into the backbone of a polymer. However, since only a small portion of the polymer is occupied by the alicyclic compound, resistance to dry etching is still weak. Also, since the alicyclic compounds are hydrophobic, if such an alicyclic compound is contained in a polymer, adhesion to materials underlying a resist layer obtained from the polymer may deteriorate.
As another conventional polymer, a cycloolefin-maleic anhydride (COMA) alternating polymer has been suggested. While the fabrication cost associated with raw materials needed to prepare a copolymer such as the COMA system is low, the yield of the polymer is noticeably reduced. Also, the transmittance of the polymer at short wavelengths, for example, 193 nm, is very low. Further, since such polymers have an alicyclic group in their backbone which is strongly hydrophobic, they have poor adhesion characteristics.
Also, due to the structural characteristics of the backbone, these polymers have a high glass transition temperature of about 200xc2x0 C. or higher. As a result, it is difficult to carry out an annealing process to remove a free volume present in a resist layer obtained from such polymers. Thus, the resist layer is susceptible to an ambient environment. For example, the resist pattern may suffer a T-top profile. Also, in post-exposure delay (PED), the resist layer exhibits a decrease in stability to an ambient atmosphere, which entails many problems in a variety of processes using the resist layer.
The present invention provides a photosensitive polymer which exhibits favorable adhesion to underlying layer materials and favorable resistance to dry etching, and which is relatively inexpensive to fabricate.
The present invention also provides a resist composition which exhibits favorable lithographic characteristics when conducting a photolithography process using a light exposure source at a short-wavelength region, e.g., 193 nm, as well as a deep UV region, e.g., 248 nm.
According to an aspect of the present invention, there is provided a photosensitive polymer comprising a copolymer having a formula 1: 
wherein x is an integer between 1 and 4 inclusive, R1 is a hydrogen atom or a methyl group, R2 is an acid-labile C4 to C20 hydrocarbon group, p/(p+q+r)=0.1 to 0.4, q/(p+q+r)=0.1 to 0.5, and r/(p+q+r)=0.1 to 0.4. The photosensitive polymer has a weight average molecular weight of 3,000 to 50,000.
Preferably, R2 is a t-butyl, tetrahydropyranyl or 1-ethoxyethyl group. Also, R2 may be an alicyclic hydrocarbon group, exemplified by a 2-methyl-2-norbornyl, 2-ethyl-2-norbonyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 2-propyl-2-adamantyl, 2-methyl-2-fenchyl or 2-ethyl-2-fenchyl group.
According to another aspect of the present invention, there is provided a photosensitive polymer comprising a copolymer having a formula 2: 
wherein x is an integer between 1 and 4 inclusive, R3 is a hydrogen atom, or a hydroxy, carboxyl, halide, nitrile, alkyl, alkoxy, sulfonate or acid-labile C4 to C20 ester group, p/(p+q+s)=0.1 to 0.4, q/(p+q+s)=0.3 to 0.5, and s/(p+q+s)=0.2 to 0.5. The photosensitive polymer has a weight average molecular weight of 3,000 to 30,000.
Preferably, R3 is a t-butyl ester, tetrahydropyranyl ester or 1-ethoxyethyl ester group. Also, R3 may be an 2-methyl-2-norbornyl ester, 2-ethyl-2-norbonyl ester, 2-methyl-2-isobornyl ester, 2-ethyl-2-isobornyl ester, 8-methyl-8-tricyclo[5.2.1.02,6]decanyl ester, 8-ethyl-8-tricyclo[5.2.1.02,6]decanyl ester, 2-methyl-2-adamantyl ester, 2-ethyl-2-adamantyl ester, 2-propyl-2-adamantyl ester, 2-methyl-2-fenchyl ester or 2-ethyl-2-fenchyl ester group.
According to yet another aspect of the present invention, there is provided a photosensitive polymer comprising a copolymer having a formula 3: 
wherein x is an integer between 1 and 4 inclusive, R1 is a hydrogen atom or a methyl group, R2 is a C4 to C20 hydrocarbon group, R3 is a hydrogen atom, or a hydroxy, carboxyl, halide, nitrile, alkyl, alkoxy, sulfonate or C4 to C20 ester group, at least one of R2 and R3 is an acid-labile group, p/(p+q+r+s)=0.1 to 0.3, q/(p+q+r+s)=0.2 to 0.5, r/(p+q+r+s)=0.1 to 0.4, and s/(p+q+r+s)=0.1 to 0.3. The photosensitive polymer has a weight average molecular weight of 3,000 to 30,000.
According to still another aspect of the present invention, there is provided a resist composition comprising a photosensitive polymer having the above formula 1, 2 or 3, and a photoacid generator (PAG).
The PAG is preferably contained in an amount of about 1.0-15 wt % based on the total weight of the photosensitive polymer. Preferably, the PAG comprises triarylsulfonium salts, diaryliodonium salts, sulfonates or a mixture of at least two of these compounds.
The resist composition according to embodiments of the present invention may further include an organic base. The organic base may be contained in an amount of about 0.01-2.0 wt % based on the amount of the PAG. Examples of the organic base include triethylamine, triisobutylamine, triisooctylamine, triisodecylamine, triethanolamine, and mixtures of at least two of these compounds.
The photosensitive polymer according to embodiments of the present invention is obtained from a copolymer of an adamantylalkyl vinyl ether monomer and maleic anhydride, providing good adhesion to underlying layer materials and high resistance to dry etching. Also, the backbone of the photosensitive polymer is more flexible than a conventional backbone, contributing to a lowering of a glass transition temperature of the photosensitive polymer. Therefore, the resist composition obtained therefrom exhibits favorable lithographic characteristics when used in photolithography processes.